1. Field of the Invention
The present invention relates to an exposure control apparatus for a camera using a recording medium in which subject images formed through a photographic lens can be electronically developed.
2. Description of Related Art
Photographic mediums in which subject images formed through a photographic lens can be electronically developed are known. One example of a photographic medium of this type is disclosed in Japanese Unexamined Patent Publication No. 4-211221. In this patent publication, a recording medium is disclosed which includes a sensitized layer on which subject images are to be formed, and a light modulating layer through which the subject images, formed on the sensitized layer, are developed. Furthermore, in this publication, an exposure control is disclosed for controlling the amount of light passed through the sensitized layer and the light modulating layer to reach a predetermined level.
It should be noted that throughout this specification, the recording medium which can be electronically developed and a camera using the same are referred to as an electronic development type recording medium and an electronic development type camera, respectively.
The detected amount of light passed through the sensitized layer and the light modulating layer varies in accordance with the variation in intensity of subject light. Therefore, a precise transmittance of the recording medium cannot be measured with the structure disclosed in the above-noted Japanese Unexamined Patent Publication No. 4-211221, and it is accordingly difficult to carry out a precise exposure control. On the other hand, exposure control precision can be improved by employing a direct photometering system such as disclosed in Japanese Examined Patent Publication No. 48-769. However, the dispersion of transmittance or gamma of the recording medium cannot be compensated since the sensitivity and the like of the recording medium are not directly detected in a conventional direct photometering system.
Another example of a photographic medium of this type is disclosed in Japanese Unexamined Patent Publication No. 2-1693. In this publication, an electronic development type recording medium is disclosed which includes a sensitized layer on which subject images are to be formed and an electric-charge holding medium through which the subject images formed on the sensitized layer are developed. With such an electronic development type recording medium, the exposure time for the recording medium can be controlled by means of controlling the voltage applied to the sensitized layer and the electric-charge holding medium.
A focal-plane shutter, which is widely used in SLR cameras, can also be used for the electronic development type camera. In an electronic development type camera having a focal-plane shutter, in a slit exposure in which the trailing blades start moving before the leading blades completely open, if an exposure control for the electronic development type recording medium is carried out by merely controlling the focal-plane shutter, a dark current occurs in the unexposed portion of the recording medium, thus resulting in the occurrence of fogging in the unexposed portion caused by the difference in exposure time due to the slit exposure.
On the other hand, even in the case where the slit exposure is not performed due to a long exposure time, if an exposure control for the electronic development type recording medium is carried out by merely controlling the voltage application to the recording medium, an electric charge occurs in the electric charge generating layer of the recording medium due to an exposure in the state where no voltage is applied, thus resulting in the occurrence of fogging. In Japanese Unexamined Patent Publication No. 3-219270 it is noted that fogging occurs in the case when a voltage is applied to the electronic development type recording medium well before the recording medium starts to be exposed and that a precise exposure control cannot be achieved by merely controlling the voltage applied to the recording medium.